Abstract: A fundamental question in cognitive science is whether animals can represent numerosity (a property of a stimulus that is defined by the number of discriminable elements it contains) and use numerical representations computationally. Here, it was shown that rhesus monkeys represent the numerosity of visual stimuli and detect their ordinal disparity. Two monkeys were first trained to respond to exemplars of the numerosities 1 to 4 in an ascending numerical order (1 --> 2 --> 3 --> 4). As a control for non-numerical cues, exemplars were varied with respect to size, shape, and color. The monkeys were later tested, without reward, on their ability to order stimulus pairs composed of the novel numerosities 5 to 9. Both monkeys responded in an ascending order to the novel numerosities. These results show that rhesus monkeys represent the numerosities 1 to 9 on an ordinal scale.

Abstract: The costs associated with initial conflicts could be reduced if animals can assess the fighting ability of possible future opponents by watching their contest success against other individuals. We tested this hypothesis by conducting repeated dyadic dominance trials on size-matched juvenile rainbow trout,Oncorhynchus mykiss. In the first trial a dyadic contest was `observed' by a single fish separated by a transparent divider. In the second trial, the observer was paired against either the `familiar' dominant fish or an unfamiliar dominant fish from the first trial. We predicted that observers should settle conflicts with previewed opponents faster and with less aggression than those with unfamiliar fish. This prediction was supported for observers that lost against a previewed competitor, since these fish reduced their aggression more rapidly than did unfamiliar observers. Familiar observers that won, however, showed a more rapid increase in aggression compared with unfamiliar winning observers. This suggests that, regardless of whether an observer challenges the initial dominant, this `decision' is taken more rapidly in conflicts with preassessed contestants, because of the a priori information about their fighting ability. Since preassessment could save energy and allow effort to be concentrated on contests with a high payoff/probability of winning, selection may favour preview strategies when contest competition over resources is important for fitness.

Abstract: The use of reaction time has a great tradition in the field of human information processing research. In animal research the use of reaction time test paradigms is mainly limited to two research fields: the role of the striatum in movement initiation; and aging. It was discussed that reaction time responding can be regarded as “single behavior”, this term was used to indicate that only one behavioral category is measured, allowing a better analysis of brain-behavior relationships. Reaction time studies investigating the role of the striatum in motor functions revealed that the initiation of a behavioral response is dependent on the interaction of different neurotransmitters (viz. dopamine, glutamate, GABA). Studies in which lesions were made in different brain structures suggested that motor initiation is dependent on defined brain structures (e.g. medialldorsal striatum, prefrontal cortex). It was concluded that the use of reaction time measures can indeed be a powerful tool in studying brain-behavior relationships. However, there are some methodological constraints with respect to the assessment of reaction time in rats, as was tried to exemplify by the experiments described in the present paper. On the one hand one should try to control for behavioral characteristics of rats that may affect the validity of the parameter reaction time. On the other hand, the mean value of reaction time should be in the range of what has been reported in man. Although these criteria were not always met in several studies, it was concluded that reaction time can be validly assessed in rats. Finally, it was discussed that the use of reaction time may go beyond studies that investigate the role of the basal ganglia in motor output. Since response latency is a direct measure of information processing this parameter may provide insight into basic elements of cognition. Based on the significance of reaction times in human studies the use of this dependent variable in rats may provide a fruitful approach in studying brain-behavior relationships in cognitive functions.

Abstract: Natural selection often promotes a mix of behavioural phenotypes in a population. Adaptive variation in the propensity to take risks might explain individual differences in shyness and boldness in humans and other species. It is often implicitly assumed that shyness and boldness are general personality traits expressed across many situations. From the evolutionary standpoint, however, individual differences that are adaptive in one context (e.g. predator defence) may not be adaptive in other contexts (e.g. exploration of the physical environment or intraspecific social interactions). We measured the context specificity of shyness and boldness in a natural population of juvenile pumpkinseed sunfish,Lepomis gibbosus, by exposing the fish to a potentially threatening stimulus (a red-tipped metrestick extended towards the individual) and a nonthreatening stimulus (a novel food source). We also related these measures of shyness and boldness to behaviours observed during focal observations, both before and after the introduction of a predator (largemouth bass,Micropterus salmoides). Consistent individual differences were found within both contexts, but individual differences did not correlate across contexts. Furthermore, fish that were scored as intermediate in their response to the metrestick behaved most boldly as foragers and in response to the bass predators. These results suggest that shyness and boldness are context-specific and may not exist as a one-dimensional behavioural continuum even within a single context.